Highly efficient and compact frontlighting for polarization-based reflection light valves

Abstract

An optical device and a display are disclosed that include an illumination source which provides unpolarized light. An array of polarizing plates have an entrance surface, which receives the unpolarized light at an oblique angle, and an exit surface which provides a polarized light having a first polarization and exiting the array at a substantially perpendicular direction to the exit surface. A light valve selectively rotates the polarized light to form an image forming light, and an imaging lens receives the image forming light and forms an image. Each of the polarizing plates in the array has opposing surfaces that are tilted relative to its entrance and exit surfaces. Each polarizing plate includes a polarizing layer formed on one of the opposing tilted surfaces, and a half-wave optical retardation layer formed on the polarizing layer.

Having thus described our invention, what we claim as new, and desire to secure by letters patent is: 
     
       1. An optical device comprising an array of polarizing plates, each one of said polarizing plates having opposing surfaces that are tilted relative to entrance and exit surfaces of said one polarizing plate, and including: a polarizing layer formed on one of said opposing tilted surfaces; and   a half-wave optical retardation layer formed on said polarizing layer;   said array of polarizing plates converting unpolarized light, which is incident on said entrance surface at an oblique angle from a normal to said entrance surface, to a polarized light having a first polarization and exiting approximately perpendicular to said exit surface.   
     
     
       2. The optical device of claim 1, wherein said array of polarizing plates is transparent to a light having a second polarization. 
     
     
       3. The optical device of claim 1, wherein a top half of said polarizing layer reflects said polarized light having said first polarization to exit from a first half of said exit surface of said one polarizing plate, and passes a light having a second polarization toward another polarizing plate adjacent to said one polarizing plate, said half-wave optical retardation layer of said one polarizing plate changing said second polarization to said first polarization, wherein said changed first polarization of light reflects from a bottom half of a polarizing layer of said other polarizing plate to exit from a second half of an exit surface of said other polarizing plate. 
     
     
       4. The optical device of claim 1, wherein a tilt angle between an axis, which is perpendicular to said entrance and exit surfaces, and said opposing surface is substantially 30 degrees, and said oblique angle is substantially 60 degrees. 
     
     
       5. The optical device of claim 1, wherein a length of said tilted surface is substantially twice a length of said exit surface. 
     
     
       6. The optical device of claim 1, wherein a cross-section of said polarizing plate is a parallelogram. 
     
     
       7. The optical device of claim 1, wherein a distance between said entrance and exit surfaces is approximately 2 mm. 
     
     
       8. The optical device of claim 1, wherein an area of said array of polarizing plates matches an area of a light valve. 
     
     
       9. The optical device of claim 1 further comprising a spatial light modulator that rotates said polarized light into an image forming light. 
     
     
       10. The optical device of claim 9, wherein said spatial light modulator is one of a transmissive and a reflective spatial light modulator. 
     
     
       11. The optical device of claim 9 further comprising a polarizer that receives said image forming light and outputs a cleaned-up image forming light for improving contrast. 
     
     
       12. The optical device of claim 9 further comprising an imaging lens that images said image forming light for viewing. 
     
     
       13. The optical device of claim 1 further comprising a light source for providing said unpolarized light. 
     
     
       14. The optical device of claim 13, wherein said light source is one of an arc lamp, a white light emitting diode, and a cold cathode fluorescent light tube. 
     
     
       15. The optical device of claim 1 further comprising a collimating lens, which is located between a light source and said entrance surface, to collimate said unpolarized light incident on said entrance surface. 
     
     
       16. The optical device of claim 1, further comprising: a light valve which receives said polarized light from said exit surface and provides an image forming light;   a beam splitter that passes one portion of said image forming light and reflects another portion thereof;   a mirror that reflects said one portion of said image forming light passed by said beam splitter back to said beam splitter, said beam splitter reflecting a portion of the light received from said mirror toward a viewer.   
     
     
       17. The optical device of claim 1 further comprising: a plurality of said array of polarizing plates, each receiving a different color component of said unpolarized light and providing a different color component of a polarized light;   a plurality of light valves each forming a different color image forming light from a respective one of said different color components of said polarized light; and   a dichroic prism which recombines said different color components of said image forming light.   
     
     
       18. The optical device of claim 17 further comprising a projection lens which projects said combined image forming light onto a screen. 
     
     
       19. The optical device of claim 17 further comprising a plurality of dichroic mirrors which separate a white unpolarized light into said different color components of said unpolarized light. 
     
     
       20. The optical device of claim 1 further comprising a prism located over said entrance surface, wherein a refraction index of said prism is substantially equal to a refraction index of said polarizing plates. 
     
     
       21. The optical device of claim 20, wherein said prism has a surface that receives said unpolarized light at a normal direction thereto, said unpolarized light continuing to said entrance surface for incidence thereon at said oblique angle. 
     
     
       22. The optical device of claim 20, wherein said prism has a surface that receives unpolarized illumination at a normal direction thereto, which is parallel to said entrance surface, and a tilted surface that reflects said unpolarized illumination to provide said unpolarized light to said entrance surface for incidence thereon at said oblique angle. 
     
     
       23. The optical device of claim 22, wherein a tilt angle between said prism tilted surface and said entrance surface allows total internal reflection of said unpolarized illumination to provide said unpolarized light to said entrance surface for incidence thereon at said oblique angle. 
     
     
       24. The optical device of claim 23 further comprising a complementary prism having a tilted surface that complements and is located over said prism tilted surface. 
     
     
       25. The optical device of claim 23 further comprising a reflective light valve that receives and selectively rotates said polarized light to form an image forming light, said reflective light valve reflecting said image forming light and a dark pixel light, said tilted surface allowing total internal reflection of said dark pixel light in a direction opposite and parallel to said unpolarized illumination. 
     
     
       26. A display comprising: an illumination source which provides unpolarized light;   an array of polarizing plates having an entrance surface, which receives said unpolarized light at an oblique angle, and an exit surface which provides a polarized light having a first polarization and exiting said array at a substantially perpendicular direction to said exit surface;   a light valve for selectively rotating said polarized light to form an image forming light; and   an imaging lens for receiving said image forming light to form an image.   
     
     
       27. A frontlighting device for a reflective light valve comprising an array of polarizing plates, each one of said polarizing plates having opposing surfaces that are tilted relative to entrance and exit surfaces of said one polarizing plate, and including: a polarizing layer formed on one of said opposing tilted surfaces; and   a half-wave optical retardation layer formed on said polarizing layer;   said array of polarizing plates converting unpolarized light, which is incident on said entrance surface at an oblique angle from a normal to said entrance surface, to a polarized light having a first polarization and exiting approximately perpendicular to said exit surface for illuminating said reflective light valve.